Published byStanford Medicine

Recent research has called into question the health benefits of regularly running for long periods of time, such as what’s done by ultra-marathoners and serial marathon runners, and a San Francisco Chroniclestory takes a closer look at the evidence.

In the piece, writer Erin Allday highlights two studies released earlier this year suggesting potential negative health effects from long-distance running, as well as research presented last month showing fewer deaths among runners who log 20 miles per week at a leisure pace compared to lose who run longer and faster. Allday writes:

[The most recent study] and others all build evidence for the U-shaped curve of exercise benefits: that greater effort begets greater benefits, but only to a certain point. Then the benefits drop off, suggesting that there’s probably a maximum amount of exercise before it starts to become unhealthy.

In another way to look at the U-curve, someone running 10 miles a week may actually be healthier than someone running 60 miles a week – and an athlete doing the 5K fun-run associated with the San Francisco Marathon may be better off, health-wise, than… the handful of other runners attempting the 52.4-mile double marathon.

While the U-curve is pretty widely accepted, there’s disagreement over how much exercise may be too much. Many scientists say, assuming there exists a maximum safe amount of running, it’s probably so high that very few runners will ever get there.